Method for in situ immobilization of water-soluble nanodispersed metal oxide colloids

ABSTRACT

The invention relates to heterogeneous catalysts which are particularly easy to produce. Said heterogeneous catalysts are generated by immobilizing preformed monometallic or multimetallic metal oxide particles in situ on an oxidic or non-oxidic carrier, wherefore metal oxide colloids which are stabilized by hydroxide ions and immobilized on carriers contained in the suspension are generated from conventional, water-soluble metal salts by means of hydrolysis and condensation. The inventive method makes it possible to produce fuel cell catalysts, for example.

This application is a divisional of U.S. Ser. No. 10/507,764 filed Sep.15, 2004, now allowed, which is a 371 of PCT/EP03/01826 filed on Feb.25, 2003.

The present invention relates to heterogeneous catalysts which areparticularly simple to prepare and are produced by in-situimmobilization of preformed monometallic or multimetallic metal oxideparticles on an oxidic or nonoxidic support.

Nanosize transition metal colloids are of great interest in catalysis.Applications are found, for example, in organic synthesis and aselectrocatalysts for fuel cells. Furthermore, they serve as buildingblocks in materials science [G. Schmid, Clusters and Colloids, VCH,Weinheim, 1994]. Numerous methods are available for preparing metalcolloids. Apart from physical methods such as metal vaporization orphotochemical or radiolytic reduction of suitable metal precursors,metal colloids are obtained mainly by reduction of customary metal saltssuch as PdCl₂, Pd(OAc)₂, H₂IrCl₆, H₂PtCl₆, PtCl₄, RuCl₃, CoCl₂, NiCl₂,FeCl₂ or AuCl₃, dissolved in water or organic solvents by means of awide range of chemical reducing agents such as complex hydrides or loweralcohols. Apart from monometallic metal colloids, bimetallic colloidsare also obtainable by means of reductive methods, but the metals usedhave to have a similar redox potential because otherwise bimetalliccolloids are not formed. The development of electrochemical processesfor preparing metal and bimetal colloids enables the use of chemicalreducing agents to be dispensed with. Variation of the electrolysisparameters allows the size of the metal colloids to be influenced in atargeted way [M. T. Reetz, S. A. Quaiser, Angew. Chem. 1995, 107, 2956;Angew. Chem., Int. Ed. Engl. 1995, 34, 2728]. Finally, the metal oxideconcept developed by Reetz et al. allows surfactant- andpolymer-stabilized metal oxide colloids to be prepared by means ofsimple basic hydrolysis of water-soluble metal salts [M. T. Reetz, M. G.Koch, J. Am. Chem. Soc, 1999, 121, 7933; DE 198525478 A]. From the pointof view of industrial relevance, a method which makes it possible fornanosize metal particles to be prepared in water as solvent and withoutcostly reducing agents has thus been developed. A further advantage ofthe metal oxide concept is the large number of accessible mixed metalsystems which cannot be prepared by means of reductive methods.

Compared to metallic colloids, comparatively little about thepreparation and properties of nanosize metal oxides is known from theliterature. Apart from the above-mentioned water-soluble metal oxidecolloids [M. T. Reetz, M. G. Koch, J. Am. Chem. Soc, 1999, 121, 7933; DE198525478 A], the preparation of MnO₂ by radiolysis of KMnO₄ has beendescribed [C. Lume-Pereira, et al., J. Phys. Chem. 1985, 89, 5772].Furthermore, polymer-stabilized RuO₂ colloids prepared from RuO₄ orKRuO₄ are known [K. Kalyanasundaram, M. Grätzel, Angew. Chem. 1979, 91,759; P. A. Christensen, et al., J. Chem. Soc., Faraday Trans. 1984, 80,1451]. IrO2 colloids are prepared by hydrolysis of H₂IrCl₆ in thepresence of a stabilizing polymer [A. Harriman, et al., New J. Chem.1987, 11, 757; M. Hara, C. C. Waraksa, J. T. Lean, B. A. Lewis, T. E.Mallouk, J. Phys. Chem. A 2000, 104, 5275; M. Hara, T. E. Mallouk, Chem.Commun. 2000, 1903].

Catalyst systems comprising more than one active component arefrequently superior in terms of performance to the correspondingmonometallic systems. Increasing attention is therefore also being paidto the targeted preparation of bimetallic and multimetallic systems incolloid chemistry. For example, mixed palladium-nickel colloids preparedby reduction using glycol and having a molar Pd/Ni ratio of 4/1displayed the highest activity in the reduction of variousnitroaromatics [P. Lu; N. Toshima Bull. Chem. Soc. Jpn., 2000, 73,751-758]. The same effect is observed in the case of mixedplatinum-rhodium colloids [K. Siepen, H. Bönnemann, W. Brijoux, J.Rothe, J. Hormes, J. Appl. Organom. Chem., 2000, 14, 549-556]. In thiscase, too, the mixed colloids (Pt/Rh=1/9) displayed the highest activityin the reduction of butyronitrile.

The positive influence of immobilization of the metal colloids is madeclear, for example, by metal colloids immobilized on carbon black orSiO₂. In the hydrogenation of 1,5-cyclooctadiene, butyronitrile,cyclohexene and crotonic acid, the heterogenized colloid catalystsdisplay a higher activity than corresponding commercial heterogeneouscatalysts [a) H. Bönnemann, G. Braun, W. Brijoux, R. Brinkmann, A.Schulze-Tilling, K. Seevogel, K. Siepen, J. Organomet. Chem. 1996, 520,143-162; b) H. Bönnemann, W. Brijoux, R. Brinkmann, R. Fretzen, T.Jouβen, R. Köppler, B. Korall, P. Neiteler, J. Richter, J. Mol. Catal,1994, 86, 129-177].

Surfactant-stabilized platinum-ruthenium colloids have also beenprepared for use as polymer electrolyte membrane fuel cell (PEM-FC)catalysts [U. A. Paulus, U. Endruschat, G. J. Feldmyer, T. J. Schmidt,H. Bönnemann, R. J. Behm, J. of Catalysis, 2000, 195, 383]. For thispurpose, platinum acetylacetonate and ruthenium acetylacetonate werereduced by means of trimethylaluminum in dry toluene under argon. Thecolloids were made water-insoluble by addition of nonionicpolyoxyethylenealkyl surfactants and, in a third step, immobilized onVulcan XC72. However, the need to work under inert gas and the manysteps necessary in this process are disadvantageous. In addition, it hasto be assumed that aluminum continues to be present in the catalystmaterial, which sometimes has an adverse effect on the actual catalysis.

In the cases described, the stabilizer is only a necessary auxiliaryreagent. It would therefore be desirable, from ecological and economicpoints of view, to be able to dispense with the stabilizer entirely inthe preparation of heterogeneous catalysts prepared from preformed metalcolloids.

An alternative approach to the preparation of heterogeneous catalysts isprovided by the known methods which are used, in particular, inindustry, e.g. absorption, precipitation and ion exchange of metal ionson support materials. Here, the active component is generated in aplurality of stages by reduction, pyrolysis, calcination, etc., onlyafter application of the respective metal ions to the support [a) A. B.Stiles, T. A. Koch, Catalyst Manufacture, Marcel Dekker, New York, 1995;b) M. Che, O. Clause, C. Marcilly in Handbook of HeterogeneousCatalysis, vol. 1, (ed.: G. Ertl, H. Knözinger, J. Weitkamp), VCH,Weinheim, 1997].

To prepare the commercial platinum-ruthenium/Vulcan XC72 catalysts forlow-temperature fuel cells, use is made mainly of a process developed byWatanabe. Here, platinum sulfite complexes are oxidatively decomposedand a ruthenium salt is simultaneously absorbed. A disadvantage is thatthe synthesis requires strict adherence to particular pH values. Only inthe last stage are the 3-4 nm platinum-ruthenium particles generated byreduction with hydrogen [M. Watanabe, M. Uchida, S. Motoo, J.Electroanal. Chem. 1987, 229, 395].

A further example is provided by fuel cell catalysts comprising up tofour metals from the group consisting of Pt, Rh, Ru, Pd, Ir. However,the multimetallic catalysts are prepared via complicated two-stageabsorption and reduction process [S. Hitomi JP 2001118582 A2, and DE10047935 A1].

The use of platinum colloids as precursors for the active component of afuel cell catalyst has also been described [Petrow et al. FR 2309045 A2,and U.S. Pat. No. 4,044,193 A]. Here, H₆Pt (SO₃)₄, a platinum salt whichis obtained beforehand as a white solid from H₂PtCl₆ by ligand exchangeand subsequent treatment with an ion exchanger is used as a source ofplatinum colloids. Disadvantages of this process are the use of theH₆Pt(SO₃)₄ salt which firstly has to be prepared by a complicatedmethod, the high costs to be expected from the use of numerous chemicals[ion exchange resin, sodium carbonate, sodium sulfite) and themultistage process which finally leads to a finished catalyst. Inaddition, only a catalyst comprising platinum as active component isobtainable by means of this process.

The use of citrate as reducing agent for preparing platinum colloids asprecursors for a fuel cell catalyst has also been described [Y. Suguru,S. Terazono, E. Yanagsawa, JP 2001093531 A2]. The platinum colloidsstabilized by means of dodecylbenzenesulfonate after reduction aredeposited on Vulcan XC72R conductive carbon black which has beenactivated beforehand by treatment with 60% strength nitric acid. Adisadvantage of this process is the necessity of using a stabilizer anda reducing agent. In addition, the active component is deposited on thestill to be activated support only in a second step.

A comparatively quick route to a finished catalyst layer for a polymermembrane electrolyte fuel cell (PEM-FC) is provided by an alternativeprocess [Hitomi, JP 200111858 A]. Here, a spreadable paste is firstlyproduced from Vulcan XC72 and the Nafion polymer. This is used toprepare a 13 μm thick film into which [Pt(NH₃)₄]Cl₂ is introduced byadsorption over a period of 24 hours. This composite is finally treatedwith hydrogen at 180° C. in order to reduce the platinum and to generatethe active particles on the support. This process is carried out twiceand excess [Pt(NH₃)₄]Cl₂ is washed out of the film using 1 Mhydrochloric acid. Disadvantages of this process are, in this case too,the necessarily multistage process with intermediate drying steps andoccurring at 180° C.

The abovementioned examples of the preparation of heterogeneouscatalysts show the general disadvantages which have not yet been solved:

1) If colloids are used as preformed active components, it is necessaryto use temporary stabilizers to prevent undesirable agglomeration. Thesubsequent removal of the stabilizer is complicated and not alwaysquantitative. In addition, the amounts of the substances which can beobtained are still too low for industrial applications.

2) Catalysts produced in the classical way frequently require a largenumber of complicated process steps.

Furthermore, the active component in its final form is obtained onlyafter the last process step.

It is therefore an object of the invention to avoid these disadvantages.

An unexpected simple way of avoiding these disadvantages is the in-situimmobilization according to the invention of metal oxide colloids formedby basic hydrolysis on an oxidic or nonoxidic support. Here, in contrastto the known methods of preparing metal or metal oxide colloids, the useof a stabilizer is dispensed with. In this way, a heterogeneous catalystwhich comprises, as active component, metal oxide particles comprisingone, two or more different, homogeneously mixed metal oxides is obtainedin a single process step after appropriate purification and drying. Theparticles have an average diameter of 0.5-5 nm, usually 1-3 nm, and areuniformly distributed over the support. This observation is all the moresurprising since it was not to be assumed that it would be possible toimmobilize colloids stabilized by negatively charged hydroxide ions in abasic solution on a support.

This process makes it possible to obtain, inter alia, supportedmultimetal oxide catalysts comprising oxides of at least three differentmetals among which one can be a main group metal, in particular Sn, andalso catalysts comprising the oxides of two metals of which one metalcan be Pt and the second can be Sn or Ir, Ru, Fe or W or anothertransition metal or one metal is Ir and the second metal is anothertransition metal. The catalysts which can be obtained by the inventiveprocess include the combinations comprising at least three transitionmetals which are of interest for fuel cell applications and in which theoxides of Pt and Ir are in each case present, and the arbitrarycombinations of at least three oxides of metals selected from the groupconsisting of Pt, Ir, Ru, Os, W, Mo, Pd and Sn, e.g. the combinationsPt/Ru/Mo, Pt/Ru/Os, Pt/Ru/Sn, Pt/Ru/Os/Ir.

Suitable transition metals are the metals of transition groups IIIb,IVb, Vb, VIb, VIIb, VIII, Ib or IIb of the PTE.

Conversion of the metal oxides into the appropriate reduced form of themetals on the support can be effected either during the later catalysisprocess or beforehand by treatment with, for example, hydrogen,hypophosphite, formate or alcohols (e.g. methanol, ethanol, etc.),without appreciable particle growth or alteration of the stoichiometrybeing observed. When electrically conductive carbon blacks are used assupports, reduction of the metal oxide particles by electrochemicalmeans is also possible. A further advantage of the method is theinsensitivity of the catalyst toward atmospheric oxygen when carbon isused as support. In contrast to, for example, platinum(0) on VulcanXC72, no spontaneous combustion of the support is observed since themetal is present in immobilized form as metal oxide.

That the process is actually an in-situ immobilization following thesynthesis of the metal oxide colloids is evidenced by a clear solutionwithout a precipitate being obtained after an appropriately shortreaction time in the absence of a suitable support and a transmissionelectron micrograph of the solution showing metal oxide particles havinga size of 1-2 nm. This corresponds to the size found for the activecomponent on the support material in a transmission electron micrograph.At an excessively long reaction time, undesirable agglomeration andprecipitation of the metal oxide is observed in the absence of a supportmaterial.

This novel process (also referred to by us as “instant process”) thusdiffers from known processes in which dissolved metal salts are firstlyapplied to a support by impregnation, precipitation or ion exchange andthe active component is only generated in its final form and size on thesupports in one or more subsequent steps. The novel process is alsoparticularly simple.

The novel method of in-situ immobilization of colloidal metal oxideshas, inter alia, the following advantages:

-   1) The use of water as inexpensive and environmentally friendly    solvent.-   2) Virtually complete conversion of the metal precursor into soluble    metal or multimetal oxides (no loss of metal).-   3) Up to 20% of metal is immobilized on the support in only one    reaction step.-   4) Preparation of virtually monodisperse, dissolved or supported    nanoparticles in the size range 0.5-5 nm, i.e. high dispersion of    the metals.-   5) The metal or multimetal oxide particles obtained by hydrolysis    and condensation display a high structural stability at high    temperatures. For example, no appreciable particle growth was    observed for platinum-ruthenium-osmium-iridium oxide particles    shaving an average size of 2 nm after treatment at 500° C. in an    XRD/DFA experiment.-   6) Concentration in space of the particles of the support surface is    not observed; instead, a uniform distribution of the active    component on the support is found.-   7) Multiple treatment of the already metal-laden support with fresh    metal salt solution makes it possible to achieve even higher    loadings with retention of the average particle size and    distribution on the support.-   8) Simple purification and isolation of the catalyst powder by    dialysis, lyophilization or centrifugation.-   9) Simple reduction of the supported metal or multimetal oxides by    means of hypophosphite, formate, hydrogen or alcohols (e.g.    methanol, ethanol, etc.) without an appreciable change in the    stoichiometry and the size distribution. In the case of particles    supported on electrically conductive carbon blacks, the catalyst can    also be reduced by electrochemical means.-   10) Problem-free handling of the supported metal oxide or multimetal    oxide catalysts in air, in contrast to the corresponding supported    metal catalysts which are subject to surface oxidation in air and    sometimes tend to ignite spontaneously.-   11) Immobilization of the active component on a support in only one    reaction step, without further work-up or activation steps.-   12) Control of the stoichiometry of the bimetals over a wide range.

According to the invention, the aqueous solution or suspension of atransition metal salt, or a mixture of two or more metal saltsM_(m)X_(n), is added to the aqueous solution of a base and a suitablesupport. The basic suspension of the metal salts and the support isintimately mixed by stirring at elevated temperature until the metaloxide colloids are completely immobilized. This leads firstly tohydrolysis of the metal salts and to condensation or cocondensation toform colloidal monometal oxides or colloidal mixed metal oxides whichare temporarily stabilized electrostatically by means of hydroxide ionspresent.M₁X_(n)+M₂X_(n)+M₃X_(n)+M₄X_(n)+ . . . +H₂O+base→[M₁M2_(M)3_(M)4Oy][OH⁻]

The colloidal particles are gradually immobilized on the support fromthe solution during the reaction, without undesirable agglomeration orsize growth of the particles occurring.[M₁M₂M₃M₄O_(y)][OH⁻]+support→M₁M₂M₃M₄O_(y)/support

Possible precursors for preparing monometal and multimetal oxides arecustomary salts of the metals of transition groups IIIb, IVb, Vb, VIb,VIIb, VIII, Ib and IIb of the Periodic Table; the same can be achievedusing one or more of these salts in combination with the salt of a metalfrom the main groups of the Periodic Table, in particular salts of tin.

Bases used are carbonates, hydrogencarbonates, hydroxides, phosphates orhydrogenphosphates of the alkali metals and alkaline earth metals, e.g.LiOH, NaOH, KOH, LiHCO₃, NaHCO₃, KHCO₃, CsHCO₃, Li₂CO₃, Na₂CO₃, K₂CO₃,Cs₂CO₃, Mg(OH)₂, MgCO₃, CaCO₃, Li₃PO₄, Na₂HPO₄, Na₃PO₄ or K₃PO₄.Preference is given to using Li₂CO₃, Na₂CO₃, K₂CO₃, CsCO₃ or MgCO₃.

The reaction temperature used for the reaction is in the range from 20to 100° C., preferably from 50° C. to 90° C.

The particle size of the nanostructured metal oxide colloids is in therange from 0.5 nm to 5 nm, preferably from 1 to 3 nm. The stoichiometriccomposition of the desired bimetal oxide and multimetal oxide colloidscan be controlled in a simple fashion via the amounts of metal saltsemployed to start with.

The colloidal metal oxides obtained and the corresponding catalysts canbe characterized by means of numerous physical methods including TEM,HRTEM/EDX, SEM/EDX, XRD/DFA, XPS, UV spectroscopy and cyclovoltammetryin the case of particles immobilized on electrically conductive carbonblacks.

Numerous oxidic and nonoxidic solids such as Al₂O₃, TiO₂, SiO₂, CaCO₃,MgO, La₂O₃, carbon black or activated carbon can be used as supports forthe water-soluble metal oxide colloids for the purpose of preparingheterogeneous catalysts.

The metal, bimetal or multimetal oxide colloids described here areemployed as catalysts or precursors of catalysts for organic chemicalreactions such as hydrogenations, oxidations or C—C and other couplingreactions. Use as electrocatalysts in fuel cells is likewise possibleand is of particular importance in view of the low production costs.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a transmission electron micrograph of the PtRuO_(x) colloidstabilized with hydroxide ions (left), and the supported PtRuO_(x)catalyst subsequently obtained therefrom (right).

EXAMPLE 1 Immobilization of Preformed Hydroxide-Stabilized PlatinumDioxide Colloids

2 ml of a saturated lithium carbonate solution and 6 ml of UHQ waterwere placed in a 20 ml GC vessel. While stirring, 1 ml of a 0.1 Mhexachloroplatinic acid stock solution was added. Finally, the solutionwas made up to 10 ml with 2 ml of UHQ water and the vessel was closed.The solution was stirred at 60° C. for 10 hours. The progress of thehydrolysis and condensation was followed UV-spectroscopically by meansof the decrease in the H₂PtCl₆ absorption at 260 nm until the UVspectrum showed no change in the plasmon band. As soon as no furtherchange occurred in the spectrum, a sample was taken for TEM. 78 mg ofVulcan XC72 carbon black were subsequently added in order to immobilizethe resulting platinum dioxide colloids stabilized by hydroxide ions.After 20 hours, immobilization on the support was complete. Thesuspension was worked up by sedimenting it in a centrifuge at 5000 rpmfor 10 minutes. The solid was washed three times with acetone/water(1/1) and centrifuged. Yield: 85.5 mg SEM/EDX: 8.72% by weight of Pt TEM(colloid): 2.0 ± 0.5 nm TEM (catalyst): 1-2 nm

EXAMPLE 2 Immobilization of Preformed Hydroxide-StabilizedPlatinum-Ruthenium Oxide Colloids

4 ml of a saturated lithium carbonate solution and 4 ml of UHQ waterwere placed in a 20 ml GC vessel. Firstly 0.05 mmol ofhexachloroplatinic acid dissolved in 1 ml of UHQ water and subsequently0.05 mmol of ruthenium trichloride dissolved in 1 ml of water were addedthereto. The solution then had a pH of about 9-10. The GC vessel wasclosed by means of a septum and the metal salt solution was stirred at60° C. for 10 hours. The progress of the reaction was followed by UVspectroscopy by means of the decrease in the H₂PtCl₆ absorption at 260nm until the UV spectrum showed no change in the plasmon band. As soonas no further change occurred in the spectrum, a sample was taken forTEM (FIG. 1: TEM at left). 78 mg of Vulcan XC72 conductive carbon blackwere subsequently added and the mixture was stirred at 60° C. for afurther 12 hours. The suspension was worked up by sedimenting it in acentrifuge at 5000 rpm for 10 minutes. The solid (FIG. 1: TEM at right)was washed three times with acetone/water=1/1 and centrifuged. Yield:38.1 mg SEM/EDX: 2.58% by weight of Pt; 1.97% by weight of Ru TEM(PtRuO_(x), colloid): 1.4 ± 0.3 nm TEM (PtRuO_(x) catalyst): 1.8 ± 0.4nmGeneral Procedures for the Preparation of the Supported CatalystsGP1 Cleaning of the Glass Apparatus Used

The glass flasks used were freed of any traces of metal by means of aquaregia before use. To remove any ground joint grease residues, the flaskswere subsequently cleaned out using a scourer under hot water and forthe same purpose rinsed with methyl tert-butyl ether.

GP2 Instant Process

In a two-neck flask which had been cleaned as described in GP1 or a 20ml GC vessel, 3 equivalents of lithium carbonate were dissolved in ⅗ ofthe volume of UHQ water necessary for a 10 mM batch. The amount ofcarbon black necessary for 20% by weight loading was added to thesolution. The desired amount of noble metal salt dissolved in ⅕ of thevolume of UHQ water was added dropwise to this suspension. The remainingamount was used to transfer the residue of the metal salt into thereaction vessel, so that a 10 mM solution, based on the total noblemetal content, was obtained. The pH of the suspension should have beenin the range from 9 to 10. The suspension was stirred at 60° C. Theprogress of the reaction was followed by means of UV spectroscopy. Thesamples were firstly centrifuged at 14 000 rpm. At the beginning, thesupernatant was diluted 1/100 and the 0.1 mM solution was measured. Assoon as no absorption or an unchanged absorption in the UV spectrum wasobserved, the reaction was complete. The suspension was centrifuged andthe solid was washed three times with water/methanol (1/1) andcentrifuged again. Finally, the laden carbon black was dried by means offreeze drying.

EXAMPLE 3 In-Situ Immobilization of Hydroxide-Stabilized Metal OxideColloids

Procedure: as Described in GP2 TABLE 1 Platinum dioxide/Vulcan catalystsprepared Carbon ^(W)metal V Platinum Li₂CO₃ black t Yield [% by d_(TEM)Cat. [ml] [mmol] [mmol] [mg] [h] [mg] weight [nm] EC13 50 0.5 1.5 400 6387.0 13.17 1.2 ± 0. EC14 100 0.9 3.0 800 10 945.0 15.12 1.6 ± 0. EC15100 1.1 3.0 800 22 1035.0 17.57 1.3 ± 0.

EXAMPLE 4 Double Direct Application of Platinum to Vulcan XC72 CarbonBlack Support EC23

In a 50 ml two-necked flask which had been cleaned as described in GP1,20 mg of the catalyst EC15 (17.57% by weight of platinum, 3.6 mg of Pt)were suspended in 18 ml of UHQ water. 1 ml of a saturated lithiumcarbonate solution was added thereto. Finally, 4.0 mg of platinum ashexachloroplatinic acid (9.3 mg of 43% by weight Pt in H₂PtCl₆ accordingto EA) dissolved in 1 ml of UHQ water were added. The suspension thenhad a pH of 10.3. The suspension was then stirred at 60° C. for 24hours. The reaction solution was purified by means of two dialysesagainst 200 ml of water and finally freeze dried. Yield: 20.3 mgSEM/EDX: 32.4% by weight of platinum TEM (EC23): 1.4 ± 0.3 nm

EXAMPLE 5 Application of the Platinum Dioxide Colloids to Various CarbonBlack Supports

Preparation as Described in GP2 TABLE 2 Immobilization of platinumdioxide colloids on various conductive carbon blacks Weight of carbonblack W_(pt) Target used [% by d_(TEM) Cat. Support loading [mg] weight)[nm] EC24 EB111 carbon 20% by 78.0 14.09 1.4 ± 0.3 black weight EC25EB111 carbon 30% by 45.5 15.06 1.6 ± 0.4 black weight EC26 N220 carbon20% by 78.0 17.59 1.8 ± 0.4 black weight EC27 EB171 carbon 20% by 78.018.69 1.6 ± 0.4 black weight EC28 N234 carbon 20% by 78.0 18.98 1.6 ±0.3 black weight EC29 N234graph 20% by 78.0 21.71 1.7 ± 0.3 carbon blackweight EC30 Printex XE2 20% by 78.0 17.78 1.3 ± 0.3 carbon black weight

EXAMPLE 6 Bimetallic, Trimetallic and Tetrametallic Systems by theInstant Method

Procedure: as Described in GP11 TABLE 3 Bimetallic, trimetallic andtetrametallic metal oxide/Vulcan catalysts prepared Vulcan carbonW_(metal) V Metal Li₂CO₃ black Yield [% by d_(TEM) Cat. [ml] [mmol][mmol] [mg] [mg] weight] [nm] EC31 20 0.10 Pt 0.6 119 81.0 8.15 Pt 1.3 ±0.3 0.10 Ru 5.08 Ru EC32 50 0.25 Pt 1.5 296 358.0 11.29 Pt 1.6 ± 0.40.15 Ir 6.56 Ir EC33 20 0.10 Pt 0.6 15 118.0 6.19 Pt 1.2 ± 0.3 0.10 Os6.89 Os EC34 100 0.68 Pt 1.5 800 824.0 13.22 Pt 1.6 ± 0.5 0.34 Ru 3.84Ru 0.34 Mo 1.92 Mo EC35 30 0.07 Pt 0.6 130 138.0 4.07 Pt 1.3 ± 0.3 0.07Ru 1.91 Ru 0.07 Os 0.33 Os EC42 60 0.15 Pt 0.7 160 229.0 18.90 Pt 1-20.06 Ru 5.57 Ru 0.02 Os 1.62 Os EC41 60 0.11 Pt 0.8 160 213.0 13.38 Pt1-2 0.10 Ru 9.14 Ru 0.03 Os 1.45 Os 0.01 Ir 1.02 Ir EC43 30 0.06 Pt 0.280 57.0 6.29 Pt 1-2 0.06 Sn 2.02 Sn

EXAMPLE 7 Reduction of the Directly Supported Platinum Dioxide Colloids

As Suspension

In a 100 ml nitrogen flask, 50 mg of the catalyst EC14 were suspended in20 ml of UHQ water. The flask was evacuated and flushed with argon threetimes. It was subsequently evacuated and filled with hydrogen three moretimes. The suspension was then stirred for 24 hours under a hydrogenatmosphere. After the reduction was complete, the water was removed bymeans of freeze-drying. TEM (EC14red): 2.3 ± 0.6 nmDry Reduction

50 mg of the catalyst EC15 were placed in a baked Schlenk flask filledwith argon. The vessel was closed and evacuated and filled with argonthree times. It was subsequently evacuated and filled with hydrogenthree more times. The catalyst was left in the hydrogen atmosphere for24 hours. The flask was then flushed with argon again and the catalystwas analyzed by means of TEM. TEM (EC14red): 2.4 ± 0.7 nm

1. A process for preparing catalysts comprising monometal oxideparticles or multimetal oxide particles having particle diameters offrom 0.5 to 5 nm and being immobilized on a support, said processcomprising the steps of: a) hydrolyzing and condensing or cocondensingin a basic aqueous solution a metal salt or a mixture of a plurality ofmetal salts to yield a solution comprising water-soluble monometal oxideor multimetal oxide colloid stabilized by hydroxide ions, wherein themetal(s) of said metal salt or said plurality of metal salts is(are)selected from the group consisting of metals of transition groups IIIb,IVb, Vb, VIb, VIIb, VIII, Ib or IIb of the Periodic Table of Elements,and b) immobilizing the resulting water-soluble monometal oxide ormultimetal oxide colloid stabilized by hydroxide ions in situ on asupport which is additionally present in suspension in the solution. 2.The process as claimed in claim 1, wherein the salt of a main groupmetal is additionally used as metal salt.
 3. The process as claimed inclaim 2, wherein the main group metal is tin.
 4. The process as claimedin claim 3, wherein the metal salt is SnCl₂ or SnCl₄.
 5. The process asclaimed in claim 1, wherein the support is selected from the groupconsisting of oxidic supports.
 6. The process as claimed in claim 5,wherein Al₂O₃, TiO₂, SiO₂, Co₃O₄, SnO₂, CaCO₃, MgO or La₂O₃ are used asoxidic supports.
 7. The process as claimed in claim 1, wherein thesupport is selected from the group consisting of nonoxidic supports inthe form of carbon black or activated carbon.
 8. The process as claimedin claim 1, wherein the basic aqueous solution comprises a base selectedfrom the group consisting of a carbonate, hydrogen carbonate, hydroxide,phosphate or hydrogen phosphate of an alkali metal or alkaline earthmetal.
 9. The process as claimed in claim 8, wherein Li₂CO₃, Na₂CO₃,K₂CO₃, Cs₂CO₃ or MgCO₃ is used as base.
 10. The process as claimed inclaim 1, which is conducted at a reaction temperature in the range from20 to 100° C.
 11. The process as claimed in claim 10, wherein thereaction temperature is in the range from 50 to 90° C.
 12. The processas claimed in claim 1, wherein a ratio of the metals in themultimetallic metal oxide particles is controlled via a ratio of themetal salts used.
 13. The process as claimed in claim 1, which furthercomprises reducing the immobilized metal oxide particles.
 14. Theprocess as claimed in claim 13, wherein said reducing is carried out byreacting the immobilized metal oxide particles with a reducing agent,and hydrogen, hypophosphite, formate or an alcohol is used as reducingagent.
 15. The process as claimed in claim 14, wherein methanol orethanol is used as alcohol.
 16. The process as claimed in claim 13,wherein electrically conductive carbon black is used as support and themetal oxide particles are reduced electrochemically.
 17. A supportedcatalyst comprising metal oxide particles which are prepared by aprocess as claimed in claim
 1. 18. A supported catalyst comprising metaloxide particles, wherein the metal oxide particles have particlediameters of from 0.5 to 5 nanometers and are immobilized on supports,wherein the particles comprise oxides: a) of at least three metals ofwhich one metal can be a main group metal and the other metals aremetals of transition groups IIIb, IVb, Vb, VIb, VIIb, VIII, Ib or IIb ofthe PTE, or b) of two metals of which: i) one metal is Pt and the othermetal is Sn or Ir, Ru, Fe or W or another metal of transition groupsIIIb, IVb, Vb, VIb, VIIb, VIII, Ib or IIb of the PTE, or ii) one metalis Ir and the other metal is a metal of transition groups IIIb, IVb, Vb,VIb, VIIb, VIII, Ib or IIb of the PTE.
 19. The supported catalyst asclaimed in claim 18, comprising oxides of at least three metals, whereinoxides of Pt and Ir and of at least one further metal of transitiongroups IIIb, IVb, Vb, VIb, VIb, VIII, Ib or IIb of the PTE are presentin the metal oxide particles.
 20. The supported catalyst as claimed inclaim 18, wherein the main group metal is tin.
 21. The supportedcatalyst as claimed in claim 18, comprising the oxides of at least threemetals selected from the group consisting of Pt, Ir, Ru, Os, W, Mo, Pdand Sn.
 22. The supported catalyst as claimed in claim 18, wherein thesupports are nonoxidic supports in the form of carbon black or activatedcarbon.
 23. The supported catalyst as claimed in claim 18, wherein thesupports are oxidic supports.
 24. The supported catalyst as claimed inclaim 23, wherein the supports are Al₂O₃, TiO₂, SiO₂, CaCO₃, MgO orLa₂O₃.
 25. The supported catalyst as claimed in claim 18, havingparticle diameters of from 1 to 3 nm.
 26. (canceled)
 27. (canceled) 28.(canceled)
 29. A process comprising hydrogenating, oxidizing or couplinga starting material in the presence of a catalyst to yield a desiredproduct, wherein the catalyst is a catalyst according to claim
 18. 30. Aprocess comprising conducting a fuel cell reaction in the presence of anelectrocatalyst, wherein the electrocatalyst is a catalyst according toclaim
 18. 31. The process according to claim 30, wherein theelectrocatalyst is a catalyst selected from the group consisting ofPt/Ru/Mo, Pt/Ru/Os, Pt/Ru/Sn and Pt/Ru/Os/Ir multimetal oxides.